A thermoplastic polymer composition comprising a thermoplastic polymer, a compound of the formula (1): (wherein, R1 and R2 represent each independently an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 18 carbon atoms, R3 represents an alkyl group having 1 to 3 carbon atoms, and R4 represents a hydrogen atom or methyl group), and a hydrocarbon, wherein 0.001 to 3 parts by weight of the compound of the formula (1) and 0.0005 to 0.008 parts by weight of the hydrocarbon are contained with respect to 100 parts by weight of the thermoplastic polymer.